A number of different products have been developed for use in conjunction with telephone lines, which operate either in parallel with a standard telephone or in place of a telephone, to send and/or receive information over the telephone line. Such products include automatic telephone answering machines, card readers, check verification devices, pre-programmed automatic dialers, and the like. Generally, power for operating these products is obtained from a power supply connected to the available alternating current power in the building or location where the product is used. Operating power for such products is not obtained from the telephone line; so that it is necessary to locate the products near a suitable wall outlet, or otherwise provide operating power in some way to these devices to permit them to send and/or receive signals over the telephone line.
U.S. Pat. No. 4,918,726 is directed to a card reader, which obtains all of its operating power directly from the telephone line itself; so that no additional or separate power supply connected to a source of power in the building is required. In the system of U.S. Pat. No. 4,918,726, the card reader is supplied with full operating power from the telephone line at all times. This is true whether the telephone associated with the reader is in its "on-hook" or in its "off-hook" condition. The amount of current which is drawn by the reader is relatively low, on the order of five milliamps. As a consequence, the reader is essentially "transparent" to a person using the telephone associated with the same line to which the reader is connected. Under some conditions of operation however, the power drawn by the reader can degrade the performance of the telephone on the line with which it is associated. The drawing of full operating power during the extended time periods when neither the telephone nor the reader are in operation, presents a small but steady drain of power from the telephone line.
It is desirable to provide a telephone line powered system, which is essentially transparent to a telephone on the line, and which operates in a low power mode until operation is initiated, whereupon a switch over to full power from the telephone line automatically is effected, with a subsequent return to a low power stand-by mode of operation.